United Nations Secretary-General Antonio Guterres said there were signs of hope in Syria following the overthrow of President Bashar al-Assad by rebel forces over the weekend.

"As we speak, we are witnessing the reshaping of the Middle East. ... We also see some signs of hope, and signs of hope namely coming from the end of the Syrian dictatorship," Guterres said during a visit to South Africa on Wednesday.

Syria was one of the most oppressive police states in the Middle East during five decades of Assad family rule.

Guterres said after meeting South African foreign minister Ronald Lamola in the capital Pretoria that the United Nations was committed to a smooth transition of power in Syria.

"It's our duty to do everything to support different Syrian leaders in order to make sure that they come together, they are able to guarantee a smooth transition, an inclusive transition in which all Syrians can feel that they belong," Guterres told reporters. "The alternative doesn't make any sense."